Suction Diffuser Purpose
A suction diffuser is a combination elbow, reducer, strainer, and straightening vane that works to provide maximum flow efficiency at the suction inlet of the pump while at the same time reducing space and fitting requirements. In addition, they remove large particulates from water and process liquids to prevent damage to pumps or other system components. Suction diffusers are found in many commercial and industrial applications.
How a Suction Diffuser Works
Suction diffusers are installed, in either a horizontal or vertical position, on the inlet of a pump to help achieve smooth inlet flow. When water comes out of an elbow or short reducer, it can start a swirling action. If that swirling action continues into the pump, there could be detrimental effects. For example, the forces at one point in the suction or the eye of the impeller could be different than on the other side, causing imbalance. If there is too much imbalance in the system, the seals or other components may be replaced too often. The vanes in a suction diffuser prevent this swirling and “diffuse” the water into the pump. In addition, suction diffusers allow for a shorter pipe entrance into the pump by removing turbulence from the process media flow and protecting the impeller and seals from being worn down quickly.
Suction diffusers also filter control loops in a system. The strainer inside a suction diffuser has a mesh basket in which the process media flows. This basket catches particles larger than the size of the holes in the mesh and allows the remaining liquid to continue flowing through the pipeline. Since particulate in the process media can damage sensitive equipment, suction diffusers are very useful in protecting a system from high repair costs.
Installing a suction diffuser at the pump inlet effectively provides pump protection, saves installation space, and reduces the demands for maintenance and service over the pump’s expected operating life.
Advantages of Installing a Suction Diffuser
- Space is saved, and additional connection points are eliminated by mounting directly to the inlet side of the pump.
- Unwanted material is prevented from entering the pump inlet by the integral strainer.
- Straightening vanes on the outlet side of the suction diffuser reduce turbulence in the flow entering the pump.
- Installation time and cost are reduced by using a component that takes the place of a strainer, reducing elbow, and entrance pipe.
Suction Diffuser vs. Strainer
Strainers remove debris from the flow to reduce the risk of damage to equipment such as pumps, chillers, and boilers. Suction diffusers are a specialized type of strainer used for direct attachment to specific pumping-equipment inlets where compact and accessible pipeline straining is needed.
Suction Diffuser Common Problems
Improper Placement
The pump should be placed close to the suction source, but there should be at least 5 to 10 pipe diameters worth of straight, unobstructed piping connecting to the pump. Never connect any components such as an elbow, reducer, valve, strainer, or suction diffuser within the final pipework run.
Clogged Strainers
A clogged strainer with a suction diffuser will present a turbulent flow profile to the pump suction. For example, if you connect an elbow directly to the pump flange, the fluid will be forced toward the outside of the elbow and will not be directed into the center of the impeller. Most pumps are designed for fluid to be evenly loaded at the center of the impeller. Otherwise, the imbalance creates stress on the pump’s bearings and seals, leading to wear and premature failure.
Suction Diffuser Maintenance
- Periodically inspect the suction diffuser for signs of leakage or corrosion.
- Regularly inspect the inlet vanes (baffles) and clean the orifice cylinder (strainer) to guard against damage to the pump.
Identifying Suction Diffusers
Many pump manufacturers offer suction diffusers as a pump system accessory. Each has its own name for these multi-function strainers, but they all serve the same purpose within a pump system.
Suction Diffusers by Manufacturer
Bell & Gossett Suction Diffuser Plus
The Suction Diffuser Plus is an angle pattern, straightening fitting that enables a pumping system to function at optimal performance parameters. It conditions the flow into the pump suction to ensure the highest possible pump efficiency retention.
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Armstrong Suction Guides
Installed on the suction side of pumps, Armstrong Suction Guides have a versatile multi-function design that saves space (up to 20% compared to traditional piping) and installation costs while protecting against debris and foreign matter damage as well as optimizing flow efficiency. 
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Taco RSP Suction Diffusers
The Taco Suction Diffuser Rear Strainer Pullout (RSP) incorporates multiple functions in one device. As a flow straightening device, it provides maximum flow efficiency at the suction inlet of the pump while at the same time reducing space and fitting requirements and eliminating the need for an equivalent length of ten pipe diameters of straight run on the suction side of the pump. As an elbow (and in some cases a reducing elbow), it offers a built-in strainer that is easily maintained and will provide years of trouble-free system performance.
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Grundfos Series SD Suction Diffusers
Grundfos Series SD suction diffusers provide and ensure a uniform flow pattern to the suction side of the pump, ensuring a stable NPSH. Additionally, the Series SD makes it possible to install the pump in a very narrow spacing as no long bends are necessary. Finally, by incorporating a cylindrical strainer, impurities are prevented from entering the pump.
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